It just so happens that some drivers are not in the RAMDISK kernel used for install, due to space limitations.

But in this case, mfi(4) is included in the full (used on the CD) RAMDISK kernel.

Right, that's an important note..

One thing that should be mentioned, the RAMDISK_CD kernel is not exactly the "full" RAMDISK kernel, that would be the one on the FTP mirrors, it does have some devices compiled into it that RAMDISK_CD does not.